Ensure local captures work correctly on macro expansion

Closes #9245

Author: José Valim

lib/elixir/lib/exception.ex

@@ -208,7 +208,7 @@ defmodule Exception do
          {_, kind, _, clauses} <- List.keyfind(defs, {function, arity}, 0) do
       clauses =
         for {meta, ex_args, guards, _block} <- clauses do
-          scope = :elixir_erl.scope(meta)
+          scope = :elixir_erl.scope(meta, true)
 
           {erl_args, scope} =
             :elixir_erl_clauses.match(&:elixir_erl_pass.translate_args/2, ex_args, scope)

lib/elixir/src/elixir.hrl

@@ -13,6 +13,7 @@
   backup_vars=nil,         %% a copy of vars to be used on ^var
   extra_guards=[],         %% extra guards from args expansion
   counter=#{},             %% a map counting the variables defined
+  expand_captures=false,   %% a boolean to control if captures should be expanded
   stacktrace=false         %% holds information about the stacktrace variable
 }).
 

lib/elixir/src/elixir_erl.erl

@@ -1,7 +1,7 @@
 %% Compiler backend to Erlang.
 -module(elixir_erl).
 -export([elixir_to_erl/1, definition_to_anonymous/4, compile/1, consolidate/3,
-         get_ann/1, debug_info/4, scope/1, format_error/1]).
+         get_ann/1, debug_info/4, scope/2, format_error/1]).
 -include("elixir.hrl").
 -define(typespecs, 'Elixir.Kernel.Typespec').
 
@@ -48,7 +48,7 @@ get_ann([], Gen, Line) -> erl_anno:set_generated(Gen, Line).
 %% Converts an Elixir definition to an anonymous function.
 
 definition_to_anonymous(Module, Kind, Meta, Clauses) ->
-  ErlClauses = [translate_clause(Kind, Clause) || Clause <- Clauses],
+  ErlClauses = [translate_clause(Kind, Clause, true) || Clause <- Clauses],
   Fun = {'fun', ?ann(Meta), {clauses, ErlClauses}},
   LocalHandler = fun(LocalName, LocalArgs) -> invoke_local(Module, LocalName, LocalArgs) end,
   {value, Result, _Binding} = erl_eval:expr(Fun, [], {value, LocalHandler}),
@@ -117,8 +117,8 @@ elixir_to_erl_cons(T) -> elixir_to_erl(T).
 
 %% Returns a scope for translation.
 
-scope(_Meta) ->
-  #elixir_erl{}.
+scope(_Meta, ExpandCaptures) ->
+  #elixir_erl{expand_captures=ExpandCaptures}.
 
 %% Static compilation hook, used in protocol consolidation
 
@@ -220,15 +220,15 @@ add_definition(Meta, Body, {Head, Tail}) ->
   end.
 
 translate_definition(Kind, Meta, {Name, Arity}, Clauses) ->
-  ErlClauses = [translate_clause(Kind, Clause) || Clause <- Clauses],
+  ErlClauses = [translate_clause(Kind, Clause, false) || Clause <- Clauses],
 
   case is_macro(Kind) of
     true -> {function, ?ann(Meta), elixir_utils:macro_name(Name), Arity + 1, ErlClauses};
     false -> {function, ?ann(Meta), Name, Arity, ErlClauses}
   end.
 
-translate_clause(Kind, {Meta, Args, Guards, Body}) ->
-  S = scope(Meta),
+translate_clause(Kind, {Meta, Args, Guards, Body}, ExpandCaptures) ->
+  S = scope(Meta, ExpandCaptures),
 
   {TClause, TS} = elixir_erl_clauses:clause(Meta,
                     fun elixir_erl_pass:translate_args/2, Args, Body, Guards, S),

lib/elixir/src/elixir_erl_pass.erl

@@ -96,7 +96,15 @@ translate({'&', Meta, [{'/', _, [{{'.', _, [Remote, Fun]}, _, []}, Arity]}]}, S)
   {{'fun', Ann, {function, TRemote, TFun, TArity}}, SR};
 translate({'&', Meta, [{'/', _, [{Fun, _, Atom}, Arity]}]}, S)
     when is_atom(Fun), is_atom(Atom), is_integer(Arity) ->
-  {{'fun', ?ann(Meta), {function, Fun, Arity}}, S};
+  case S of
+    #elixir_erl{expand_captures=true} ->
+      Vars = [{list_to_atom("arg" ++ integer_to_list(Counter)), [], ?MODULE}
+              || Counter <- tl(lists:seq(0, Arity))],
+      translate({'fn', Meta, [{'->', Meta, [Vars, {Fun, Meta, Vars}]}]}, S);
+
+    #elixir_erl{expand_captures=false} ->
+      {{'fun', ?ann(Meta), {function, Fun, Arity}}, S}
+  end;
 
 translate({fn, Meta, Clauses}, S) ->
   Transformer = fun({'->', CMeta, [ArgsWithGuards, Expr]}, Acc) ->

lib/elixir/test/elixir/kernel/macros_test.exs

@@ -34,6 +34,10 @@ defmodule Kernel.MacrosTest do
     quote(do: 1 + unquote(value))
   end
 
+  defmacro my_macro_with_capture(value) do
+    Enum.map(value, &by_two/1)
+  end
+
   test "require" do
     assert Kernel.MacrosTest.Nested.value() == 1
   end
@@ -42,7 +46,7 @@ defmodule Kernel.MacrosTest do
     assert Nested.value() == 1
   end
 
-  test "local but private macro" do
+  test "local with private macro" do
     assert my_private_macro() == 4
   end
 
@@ -54,6 +58,10 @@ defmodule Kernel.MacrosTest do
     assert my_macro_with_local(4) == 17
   end
 
+  test "local with capture" do
+    assert my_macro_with_capture([1, 2, 3]) == [2, 4, 6]
+  end
+
   test "macros cannot be called dynamically" do
     x = Nested
     assert_raise UndefinedFunctionError, fn -> x.value end